The fearless 5-foot-7 transfer from Oklahoma, made two clutch floaters in the lane, then grabbed a crucial rebound and sank two free throws to finish a six-point flurry in the final two minutes to help ninth-seeded Musketeers beat eighth-seeded Brigham Young 79-77 in the first round of the South Regional Thursday night.

"That's his nature. He comes from a basketball family. He comes from a high school program that breeds toughness," Xavier coach Sean Miller said. "You don't have to tell a player like that what to do at the end of a game."

Justin Doellman scored 23 points and Lavender finished with 17 to help Xavier (25-8) advance beyond the first round for the fourth time in its last five NCAA appearances. The Atlantic 10 co-regular season champions will face top-seeded Ohio State and former Musketeers coach Thad Matta in the second round.

"It's hard enough to make the tournament. It's even harder to advance. We're glad to be in the seat we're in," said Miller, who was associate head coach under Matta at Xavier for three years.

"Clearly they're not 31-3 because they're OK. They're 31-3 because they're a terrific team, well coached, in a system they believe in. We're going to try our best. It's going to be a difficult task."

Xavier trailed by as many as nine before Lavender, Doellman and B.J. Raymond hit 3-pointers during a 16-3 run that turned a 52-44 deficit into a 60-55 lead. BYU (25-9) battled back to take a 73-71 lead with 2:10 to go, but couldn't stop Lavender down the stretch.

Mountain West Conference player of the year Keena Young led BYU with 24 points, including a layup at the buzzer. Mike Rose scored 15 on 3-pointers and Austin Ainge added 12 for the Cougars.

BYU has not made it out of first round of the NCAA Tournament since 1993 when it beat SMU before losing to Kansas in the round of 32. The Cougars also made quick exits in 1995, 2001, 2003 and 2004.

Ainge, the son of former BYU and NBA star Danny Ainge, said the Cougars fifth consecutive first-round loss does not detract from a rewarding season that saw the Cougars win the Mountain West regular season title -- BYU's first outright conference crown since 1988.

"I don't think it takes away from that, but it left something unfinished," Ainge said. "It's a goal we put at the end of the year. We didn't quite get it done, and that hurts."

Although beating BYU hardly is a major upset, Xavier has a solid history of success against higher seeded teams in the tourney.

The Musketeers advanced to the round of eight as a No. 7 seed three years ago, and anyone who thinks they might be intimidated facing Ohio State needs to know this: the Musketeers feel they're capable of playing with anyone after going 5-1 during the regular season against teams that made this year's tournament.

Matta was coaching Xavier when the Musketeers advanced beyond the first round in 2002, 2003 and 2004. He left the Cincinnati school for Ohio State a few months after leading the improbable run to the regional finals three years ago.

Ainge, who took over BYU's starting point guard role after Rashaun Broadus was suspended in early January, made 3 of 7 shots in the opening half, including a 3-pointer that put the Cougars up 38-32 at the half.

The 6-foot-2 senior only averaged 7.8 points this season, but has been more of an offensive threat lately. He's scored in double figures in seven of the last nine games after doing it just seven times in BYU's first 24.

The Cougars looked like they might ready to put an end to their recent tournament frustrations when Young delivered three quick baskets and Jimmy Balderson hit a 3-pointer during a spurt that carried BYU to a 49-40 lead.

Lavender's floater tied it at 73, then the Xavier point guard made another for a 75-73 lead. After BYU tied for the last time on Lee Cummard's putback, Xavier went ahead for good on Josh Duncan's layup with 34.2 seconds left.

"We had a lot of times," Young said, "where we should have made plays and closed the game out."